diff --git a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
index 4ac7f8bdbd..818f4b21dd 100644
--- a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
+++ b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
@@ -583,7 +583,9 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api.Plugins
                 ts.next =
                     DateTime.Now.ToUniversalTime().AddSeconds(ts.interval);
 
-                SenseRepeaters.Add(ts);
+                lock (SenseRepeatListLock)
+                    SenseRepeaters.Add(ts);
+                
                 idx += 6;
             }
         }